The present invention concerns a driving unit including an electric motor and a planetary gear provided with an input shaft driven by said motor and an output shaft, said unit being provided with a cooling circuit for said motor including a positive displacement pump assuring the flow of a liquid in said circuit, the planetary gear including three main elements, namely: a sun wheel, a planet wheel carrier provided with several planet wheels, and a ring gear having an inner toothing meshed with said planet wheels, one of said three main elements being connected to the input shaft, another element being connected to the output shaft and the third acting as a reaction element.